Bone matrix is known to contain a number of proteins which influence the behavior of various cell types. Some bone matrix proteins stimulate or inhibit the replication of bone cells (Farley et al Biochem., 21: 3508-3513, 1982; Sampath et al, Experimental Cell Res. 142: 460-464, 1982, and Puzas et al, Proc. Soc. Exp. Bio. and Med. 166: 113-122, 1981). Other bone matrix proteins stimulate collagen synthesis in bone cells (Canalis et al, Science 210: 1021-1023, 1980). Bone matrix, proteins such as Alpha.sub.2 HS glycoprotein, osteonectin, and Type 1 collagen are chemotatic factors for monocytes and macrophages (Malone et al, J. Cell Bio. 92: 227-230, 1982; Minkin et al, Metabolic bone Disease and Related Res. 2: 363-369, 1981).
Cartilage, but not bone, will form in pieces of muscle grown directly upon demineralized bone matrix. Demineralized bone matrix or bone matrix gelatin implanted in muscle pouches in vivo or implanted in diffusion chambers in muscle pouches in vivo is capable of recruiting native mesenchymal cells and inducing bone formation (Urist et al, Arch. Surg. 112: 612-621, 1977; Nogami et al, Clin, Orthopaedics 103: 235-247, 1977).
U.S. Pat. No. 4,294,753 discloses a process for obtaining a water-insoluble bone morphogenic protein (BMP) whose action is analogous to bone matrix gelatin in that it stimulates cartilage and bone formation when implanted in a muscle pouch in vivo.